Synthesis of tungsten-doped MFI zeolite membranes with improved performance for CO2/N2 separation

The separation of CO2 from N2 using MFI-type zeolite membranes relies on a mechanism dominated by adsorption and diffusion processes. In this investigation, we employed a tungsten (W) doping approach to elevate the CO2 separation selectivity of MFI zeolite membranes. Isothermal adsorption assessments demonstrated an elevated heat of adsorption (Qst) for CO2 and a reduced pore sizes after W doping, corroborating the enhanced CO2/N2 separation efficiency observed. Specifically, the W-doped MFI membrane exhibited a selectivity of 38.8 under dry conditions, a substantial improvement over the 8.7 selectivity achieved by the undoped Si-MFI membrane, while the CO2 permeance remained comparable (3.9 x 10-7 vs 4.5 x 10-7 mol m-2 s-1 & sdot;Pa-1). Furthermore, the incorporation of tungsten curtails the formation of silanol groups by stabilizing the zeolite framework via energetically favorable W-O-Si linkages. These linkages diminish silanol-related defects, typically prone to water adsorption, thereby enhancing the membrane's hydrophobicity. Consequently, the W-doped MFI membrane maintains a CO2/N2 selectivity of 29.5 and a CO2 permeance of 1.8 x 10-7mol m-2 s-1 & sdot;Pa-1 in the humid environments, outperforming most reported zeolite membranes and showing potential ability for practical post-combustion carbon capture applications.